Oooof. That is annoying. p5js.org just 1) completely broke the fullscreen view of sketches (even if you navigate there directly, not in an iframe), and 2) introduced one of these stupid* “accept cookies” banners. Unfortunately the latter is difficult to deal with because browsers will not send cookies with requests generated from within an iframe that is hosted on a site with a different domain name. So if p5js.org insists on having this “accept cookies” banner present on the full screen editor page then that is always going to show up, but they will hopefully fix the fact that they basically completely broke the page even after you dismiss the banner or load the page in a context were cookies are sent.
Good news: now that the preview.p5js.org domain is whitelisted you can switch to the https://preview.p5js.org/{{UserName}}/embed/{{SketchId}} style URL for your iframes and this will work because this page does not require cookies and isn’t broken. The only downside is it doesn’t have the “view code” button.
*<rant>
All of these “accept cookies” banners are absolute worthless BS that has been foisted on the entire world by the misinformed, misguided, nanny state that is the EU. Cookies are just how the internet works! If you don’t like it, disable them completely in your browser (and have fun not being able to log in to websites or add items to your shopping cart). Cookies are part of the HTTP standards for a good reason. Consent banners do absolutely nobody any good whatsoever. They are just a huge nuisance. If you live in the EU I beg you to contact your MEPs immediately and tell them that they need to completely repeal this garbage legislation. If they don’t do so, then please vote for some MEPs that actually understand web technology, instead of these medieval luddites!
</rant>